The present invention relates to a heating apparatus and method and, more particularly, to a technique for supporting an object to be heated such as a glass plate and subjecting it to a uniform temperature process in order to uniformly heat it.
Conventionally, in a heating apparatus for uniformly heating an object to be heated, as shown in FIG. 37, a plurality of cartridge type rod heaters 213 are inserted in a plate 212 made of one material. Outputs from the rod heaters 213 are controlled by a controller 214 by referring to a temperature obtained by at least one temperature sensor (not shown) provided to the plate 212, thereby heating an object 1 to be heated. To decrease in-plane temperature nonuniformity of a heating surface 212a of the plate 212, a material such as an aluminum alloy having a large thermal conductivity is used. To prevent deformation of the plate 212, a material such as stainless steel having a small thermal conductivity and a large rigidity is used. Although a materials such as ceramics with a large thermal conductivity is an ideal material for use as the plate 212, ceramics is very hard to machine and expensive.
When a material having a large thermal conductivity is used to form the plate 212, if the plate 212 is, e.g., a 400-mm square aluminum alloy plate, a temperature distribution of xc2x13xc2x0 C. or less near 200xc2x0 C. and xc2x15xc2x0 C. or less near 400xc2x0 C. is achieved by controlling the rod heaters 213.
When a material having a small thermal conductivity but a large rigidity is used to form the plate 212, if the plate 212 is a 400-mm square plate, warp of the plate 212 is suppressed to 0.2 mm or less even after the plate 212 is subjected to a heat cycle of 400xc2x0 C. or more.
As an apparatus for heating a flat plate such as a glass plate, one disclosed in Japanese Patent Laid-Open No. 10-55754 filed by the present applicant is available. The invention of this reference relates to a technique for adhering and heat-bonding two flat glass plates through a spacer. According to this technique, the flat glass plates are heated to a predetermined temperature by heating flat plates and are heat-bonded to each other.
Each heating flat plate of the above apparatus incorporates a heating means in itself and is supported on the base of the apparatus with a support member. In the apparatus shown in the above reference, the support member is made of a heat insulating material such as a ceramic member to cope with high temperatures.
In order to suppress thermal deformation of the plate 212 and to reduce its heat capacity and temperature distribution, if the plate of the heating apparatus is a 400-mm square plate, an in-plane temperature distribution of xc2x13xc2x0 C. or less near 200xc2x0 C. and xc2x15xc2x0 C. or less near 400xc2x0 C. is achieved. Even after the plate 212 is subjected to a heat cycle from room temperature to 400xc2x0 C. or more, warp of the plate 212 must be suppressed to 0.2 mm or less.
A glass plate used in, e.g., a liquid crystal display, often undergoes a heating process in the display fabrication process. To process the display or to form and assemble elements at predetermined positions on a glass plate, deformation of the glass plate caused by heat must be prevented to increase positional precision and to increase processing precision and assembling precision. For this purpose, in the heating apparatus, the glass plate must be heated by using a plate having a least possible temperature distribution.
When forming display pixels and an optical filter on a glass plate, as the positional precision of each pixel and filter largely influences the image quality of the display, the glass plate as a substrate where pixels and filter are to be formed should not largely thermally deform by a positional error factor, i.e., a temperature nonuniformity or temperature gradient.
For example, when a glass plate having a length L=400 mm is heated from 20xc2x0 C. to 220xc2x0 C., it expands by xcex94Txc3x97Lxc3x97xcex1=(220xe2x88x9220)xc3x97400xc3x97(10xc3x9710xe2x88x926)=800 xcexcm where the coefficient of expansion of glass is xcexc=10xc3x9710xe2x88x926. At this time, if a temperature distribution (nonuniformity) exists and a temperature gradient of 20xc2x0 C. exists per 400 mm, xcex94Txc3x97Lxc3x97xcex1/2=20xc3x97400xc3x9710xc3x9710xe2x88x926/2=40 xcexcm occurs, and a positional error of 40 xcexcm occurs as compared to a case wherein the temperature is uniform. Depending on the precision required by the process, element formation, and assembly, the temperature gradient must be set to 10xc2x0 C. or less. If the temperature increases uniformly and the glass plate expands uniformly, the actual or desired positions of the respective portions of the glass surface after deformation can be predicted. If irregular temperature nonuniformity or temperature gradient occurs, the glass plate deforms irregularly or nonuniformly. Then, it is difficult to predict the position of a desired portion of the glass plate.
For example, as the size of the display increases, the area of the object to be heated, e.g., a glass plate used in the display, increases, and the area of the plate of the heating apparatus also increases. When the area of the heating apparatus increases, the heat capacity increases naturally, leading to an increase in power consumption of the heating apparatus and an increase in heating and cooling times. For cooling, it is indispensable to increase the cooling capability and to add a cooling means. Hence, in the heating apparatus, particularly in relation to increased area of the object to be heated, temperature distribution of the heating apparatus must be minimized, as described above, and its heat capacity must be designed as small as possible.
When the area of the plate increases, in the above prior art, since the cartridge heaters are inserted in the tunnel holes formed in the plate, the depth of the holes and the length of the cartridge heaters increase. As for the hole depth, increasing the depth while maintaining the same diameter as that of the prior art is technically difficult, and highly precise hole formation is limited in depth. If the hole diameter is increased, while the processability increases and a deep hole can be formed easily, the plate thickness increases and the weight and heat capacity increase, leading to an increase in power consumption and heating and cooling times. For the heater, a length with which the heater can be fabricated with good precision for a certain diameter is limited. If the heater length increases, the heater diameter must be increased. As a result, the thickness of the plate into which this large-diameter heater is to be inserted increases. In this manner, if the area is increased without taking any special measure, the plate thickness increases due to limitations on the hole and heater, and the heat capacity increases more than the area increase. In other words, an issue of realizing a large plate area without increasing the heat capacity per unit area of the plate arises.
Along with a further increase in area of the plate of the heating apparatus, it has become necessary to enable free selection of the portion (region) to be heated by each heater and to perform temperature control of each heater separately, thereby reducing temperature distribution. For example, the temperature of the periphery of the plate decreases due to heat dissipation from the sidesurface. When outputs from heaters provided to the periphery of the plate are separately controlled to uniform the temperature, temperature distribution can be reduced. In the prior art, however, since the heaters are inserted in one direction of the plate, the thickness of the plate of the heating apparatus must be increased to prevent interference between the heaters in two directions, and the heaters must be set at different heights. As a result, the weight of the plate increases to increase its heat capacity, leading to an increase in power consumption and heating and cooling times. To enable a further plate area increase, temperature uniformity, and a small heat capacity, the heaters must be arranged at desired regions without increasing the plate thickness.
When a member to be heated is placed on a flat plate having a heating means and is heated, if the size of the member to be heated increases, the size of the heating flat plate increases accordingly. As a result, uniforming the heating state of the flat plate becomes difficult, and maintaining high flatness of the flat plate also becomes difficult.
Furthermore, the heating temperature must be increased depending on the material of the member to be heated to be heated. When the temperature of the flat plate also increases, maintaining high flatness of the flat plate becomes difficult.
In particular, when a glass material or the like is to be heated, as the heating temperature of the flat plate is high, the temperature of the flat plate is thermally transferred to the support member of the flat plate to expand it, affecting the flatness of the flat surface. As a result, the flatness of the flat plate suffers to impair the precision of heat bonding of the member to be processed.
In order to cope with the above problems, a measure must be taken against any temperature increase of the support member that supports the flat plate.
More specifically, to maintain high flatness of the flat plate, a plurality of support members must be provided to support the flat plate to increase the supporting rigidity, thereby maintaining high flatness of the heating flat plate.
For this purpose, the conditions for expansion and contraction of the respective support members must be set equal. However, depending on differences in structure of the respective support members, the heat capacities of the support members differ, and it is difficult to set equal conditions for expansion of all of the respective support members.
In the conventional heating apparatus, if a plate made of a material having a large thermal conductivity is used in order to decrease temperature nonuniformity, warp of the plate increases. On the other hand, if a plate made of material having a large rigidity is used to decrease warp of the plate, temperature nonuniformity of the plate increases. In other words, with the conventional heating apparatus, temperature nonuniformity and warp of the plate cannot both be solved at the same time.
An object to be heated is often influenced by a change in shape of the plate of the heating apparatus in contact with it. When the plate of the heating apparatus has a warp of 200 xcexcm or more, a gap is formed between the plate and the object to be heated. Then, the object temperature becomes nonuniform and positional precision degrades. When the object to be heated is made of glass or the like, the object to be heated itself thermally deforms in accordance with the shape of the warped plate to degrade the processing precision. Therefore, any warp of the plate of the heating apparatus must also be minimized.
To decrease temperature nonuniformity of the heating apparatus, the heat capacity of the plate of the heating apparatus must be increased. If, however, the heat capacity of the plate of the heating apparatus is large, the heating and cooling times of the heating apparatus prolong. To shorten the heating time, the power consumption of the rod heaters that heat the heating apparatus must be increased. To shorten the cooling time, another cooling means must be provided, or the cooling capability of the existing cooling means must be increased. To heat a larger, heavier object in the future, a large heating apparatus, especially a heating apparatus for heating a large area, is required. Such a heating apparatus must have a larger power consumption since its heat capacity increases. An increase in power consumption leads to an increase in size and cost of the power facility. Under these circumstances, a reduction in the heat capacity of the plate of the heating apparatus is sought for.
The present invention has been made in view of the problems described above, and has as its object to provide a heating apparatus that can realize a large area in order to improve the thermal processing precision of the object to be heated without increasing the weight and heat capacity per unit area of the heating plate.
It is another object of the present invention to provide a heating apparatus and method in which unwanted thermal deformation of the object to be heated can be uppressed so that the thermal processing precision is improved, the apparent heat capacity is decreased to shorten the preheat time required before the start of heating, and the power consumption of the heating apparatus can be decreased.
It is still another object of the present invention to provide a heating apparatus in which heaters are located at desired regions so, even if the area of the plate is further increased, any temperature distribution can be reduced.
In order to achieve the above objects, according to the present invention, there is provided a heating apparatus characterized by having a heating member obtained by stacking at least first and second plates to heat a plate-like object to be heated, and a heater serving as a heat source of the heating member, the first plate having a larger thermal conductivity than the second plate and the second plate having smaller creep than the first plate.
In order to solve the above problems and to achieve the above objects, according to the present invention, there is provided a heating apparatus for placing a flat plate-like object to be heated on a support surface and heating the object to be heated with heating means from a support surface side, characterized in that the heating means comprises a heating member that forms the support surface by stacking first and second plates, and a heater provided to the heating member as a heat source, the first plate being made of a metal material having a larger thermal conductivity than the second plate, and the second plate being made of a metal material having smaller creep as change amount caused by heat than the first plate.
Preferably, there is provided a heating apparatus for placing a flat plate-like object to be heated on a support surface and heating the object to be heated with heating means from a support surface side, characterized in that the heating means comprises a heating member obtained by stacking a second plate that forms the support surface, a first plate, and an auxiliary plate to sandwich the first plate, and a plurality of rod heaters detachably provided as a heat source in holes formed in the first plate, the first plate being made of a metal material having a larger thermal conductivity than the second plate and the auxiliary plate, and the second plate and the auxiliary plate being made of a metal material having smaller creep as change amount caused by heat than the first plate.
Preferably, there is also provided a heating apparatus for placing a flat plate-like object to be heated on a support surface and heating the object to be heated with heating means from a support surface side, characterized in that the heating means comprises a heating member that forms the support surface, and a plurality of rod heaters provided as a heat source in the heating member, and that the apparatus further comprises a plurality of support members for heating the heating means on a base member and arranged to be movable with respect to the base member, and temperature control means for performing separate temperature control operation for the support members to maintain parallelism of the heating means.
Preferably, there is provided a method of heating a flat plate-like member to be heated, characterized in that the member to be heated is placed on a flat plate, the flat plate is supported by a plurality of support members, a temperature state of the support members upon heating operation of the flat plate is measured, a temperature of the support members is controlled on the basis of measured information to guarantee a given flatness of the flat plate with the support members, thereby heating the member to be heated on the flat plate.
Preferably, there is provided a heating apparatus characterized in that, in order to integrate first and second glass plates through a frame provided at edge portions thereof and to fix a spacer member on the first glass plate at a predetermined position in a space of the frame with low-melting glass in advance, heating operation is performed by heating means formed by stacking a first plate provided with a heater and a second plate.
There is also provided a heating apparatus for placing a flat plate-like object to be heated on a support surface and heating the object to be heated with heating means from a support surface side, characterized in that the heating means comprises a heating member obtained by stacking a second plate that forms the support surface, a first plate, and an auxiliary plate to sandwich the first plate, and a plurality of rod heaters detachably provided as a heat source in holes formed in the first plate, the first plate being made of a metal material having a larger thermal conductivity than the second plate and the auxiliary plate, and the second plate and the auxiliary plate being made of a metal material having smaller creep as change amount caused by heat than the first plate, and that the apparatus further comprises a flow path formed in the second plate or the auxiliary plate to pass a coolant therethrough.
With the above arrangement, the first plate having a larger thermal conductivity than the second plate and the second plate having smaller creep than the first plate are stacked, so that any warp of the first plate resulting from heat of the heaters is suppressed by the second plate having smaller creep, and the object to be heated is heated by the first plate having a larger thermal conductivity without producing temperature nonuniformity in its heated surface. As compared to a heating apparatus using only the second plate having a smaller thermal conductivity, since the first plate having a larger thermal conductivity is used, the apparent heat capacity decreases, and the preheat time until the start of the thermal process can be shortened.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.